1. Field of the Invention
The present invention relates to a knock control apparatus for internal-combustion engine, which detects ionization of combustion gas produced by combustion in an internal-combustion engine as ionic current, judges occurrence of a knock based on output from an ionic current detection device for detecting its combustion state, and performs control in order to avoid the knock.
2. Description of Related Art
In an ignition type internal-combustion engine (hereinafter, referred to as engine), a mixture of air and fuel to be introduced into a combustion chamber (hereinafter, referred to as cylinder) is compressed by a piston, and is burned by igniting with an ignition plug to take out power. The engine output and ignition timing relative to the cylinder position are closely related to each other, and generally when the ignition timing is advanced, high output can be obtained. In the case of excessive spark-advance, an abnormal combustion state called xe2x80x9cknocking (knock)xe2x80x9d occurs, and if the knocking continuously occurs, the engine may be broken.
When the mixture is burned within the cylinder, combustion gas is ionized, and therefore, when voltage is applied to it, current flows by the ionic action. This current is called xe2x80x9cionic current,xe2x80x9d and sensitively varies in accordance with the combustion state within the cylinder. Therefore, it has been known that the combustion state (knocking state) can be detected by detecting the ionic current.
The ionic current is abruptly increased immediately after the ignition, and reaches the peak in a short time, and then gradually decreases. In the case where knocking occurs, a vibration component of several kHz is superimposed on the ionic current. On the basis of result of extraction of the vibration component corresponding to the knocking from the ionic current, the occurrence of knocking is judged, whereby when retard of the ignition timing is performed, high output can be obtained with the strength of the knocking and the frequency of its occurrence restrained.
As regards a knock control apparatus using ionic current, there has been previously proposed, by the present patent applicant, a knock control apparatus for internal-combustion engines provided with failure judgment means for judging an ionic current detection system for failure on the basis of, for example, the output from knocking strength detection means. When the output state of noise from each cylinder is judged in an operating range, in which noise ought to be detected, and the noise pulse output is obviously small, or when the filter value exceeds a predetermined value, this failure judgment means judges the cylinder concerned to be abnormal. Also, a retard angle for each cylinder will be determined in accordance with the number of cylinders which have been judged abnormal.
Hereinafter, with reference to FIG. 6, the detailed description will be made of a conventional example.
FIG. 6 is a flowchart showing failure judgment and control during failure according to the conventional example.
First, it is judged whether or not the operating condition is within a noise pulse judgment range (Step S1). If the noise pulse number is abnormally low or 0 (Step S3), this cylinder will be fail-judged (Step S4). Next, it is judged whether or not the operating condition is within a range in which the filter value is judged to be rising (Step S2). If the filter value is abnormally rising (Step S5), the cylinder will be fail-judged (Step S6).
Subsequently, the current number of fail cylinders is counted (Step S7), and it is judged whether or not the number of fail cylinders is equal to or less than a predetermined number of cylinders (Step S8). If not, the knock control will be inhibited to set a sufficient retard angle to all the cylinders (Step S12). If the number of fail cylinders is equal to or less than the predetermined number of cylinders, an average retard angle of the cylinders which are judged normal will be calculated (Step S9). A corrected retard angle corresponding to this cylinder will be acquired (Step S10), and the retard angle corresponding to this fail cylinder will be operated and set on the basis of the average retard angle of normal cylinders and the corrected retard angle (Step S11).
By the use of the knock control apparatus for internal-combustion engines proposed previously, it is possible to inhibit judgment of knocking for avoiding misjudgment of knocking and to perform ignition timing control based on safe ignition timing when, for example, high frequency noises are superimposed on ionic current to output a large quantity of noise signals, and when ionic current in some cylinders cannot be detected because of disconnected wiring in a vehicle body, failure of an ionic current detection circuit or the like.
In the conventional examples, however, there has not been proposed such a process as to stop failure judgment for returning to ordinary knock control when the detection state is continuously monitored and a normal state is recognized even after the failure judgment is performed. Therefore, for example, in the case where the engine is operated at a rich air fuel ratio, when soot temporarily adheres to plugs, when temporarily affected by radio wave of high intensity, when the engine has returned to a normal state by replacing the plugs although plug contamination advances and the degree of noise superimposition increases, or the like, temporarily noise superimposition has occurred, but when it is solved, the failure judgment cannot be stopped, but the engine cannot be returned to normal knock control.
In the case where the engine is operated at a rich air fuel ratio, when soot temporarily adheres to the plugs or the like, it has been experimentally found out that no noise superimposition occurs for each ignition, nor is the filter value so much raised, and it is difficult to judge failure by the filter value raised.
The present invention has been achieved in order to solve the above described problems, and is an object to obtain a knock control apparatus for internal-combustion engines having a function of judging whether or not the causes for failure have been solved for returning to ordinary knock control at the time of the solution, and capable of easily judging failure even in a failure mode in which it is difficult to raise the filter value and it is difficult to judge the failure in the conventional examples.
According to the invention of claim 1, there is provided a knock control apparatus for internal-combustion engines, provided with: ionic current detection means for generating a signal corresponding to knocking based on the ionic current; background level setting means for filter-processing a knock detected signal value from the ionic current detection means to set a background level, which serves as a knocking criterion, based on the filter value; knock suppression and control means for judging the knocking based on the knock detected signal value and the background level to control at least ignition timing retard; and fail control means for performing control when knock detection cannot be properly performed, wherein the fail control means is provided with: failure judgment means for judging failure for each cylinder based on output from the background level setting means and the knock suppression and control means; number of fail cylinders judgment means for judging a number of fail cylinders based on the output from the fail judgment means; retard angle changing means for changing at least the retard angle of a fail cylinder based on the output from the knock suppression and control means, the fail judgment means and the number of fail cylinders judgment means; and normal judgment returning means for returning to normal ignition timing retard when a cylinder during fail judgment meets normal judgment requirements based on the output from the background level setting means and the retard angle changing means. According to such structure, there are effects that it is possible to return to failure judgment for each cylinder, retard during failure, and normal knock control during normal judgment.
According to the invention of claim 2, there is provided a knock control apparatus for internal-combustion engines specified in claim 1, wherein the failure judgment means judges, to be defective, a cylinder having a retard angle, which is a predetermined angle or more larger than a minimum value among retard angles of each cylinder. According to such structure, there is an effect that it is possible to judge, to be defective, a cylinder which has an obviously erroneous retard angle.
According to the invention of claim 3, there is provided a knock control apparatus for internal-combustion engines specified in claim 1, wherein the background level setting means performs the filter processing for each cylinder and the failure judgment means judges, to be defective, a cylinder whose filter value exceeds a predetermined value. According to such structure, there is an effect that it is possible to judge, to be defective, a cylinder having a large degree of superimposed noise on ionic current.
According to the invention of claim 4, there is provided a knock control apparatus for internal-combustion engines specified in any of claim 1, wherein if the number of fail cylinders exceeds a predetermined number of cylinders, the retard angle changing means nullifies the retard angles for all the cylinders with respect to the ignition timing control and corrects the ignition timing for all the cylinders by the use of a predetermined retard angle. According to such structure, there is an effect that it is possible to operate the engine with safe ignition timing if the knock control performance cannot be secured because of excessive fail cylinders.
According to the invention of claim 5, there is provided a knock control apparatus for internal-combustion engines specified in claim 4, wherein the predetermined retard angle is set at least based on either the intake temperature or the engine cooling water temperature. According to such structure, there is an effect that it is possible to control ignition with safe ignition timing on the spark-advance side avoiding any excessive phase lag.
According to the invention of claim 6, there is provided a knock control apparatus for internal-combustion engines specified in claim 1, wherein if the number of fail cylinders is under a predetermined number of cylinders, the retard angle changing means nullifies the retard angles for the fail cylinder with respect to the ignition timing control and sets the retard angle for the fail cylinder based on the retard angle for a cylinder, which has not been judged to be defective, to correct the ignition timing for the cylinder concerned based on the retard angle for the fail cylinder. According to such structure, there is an effect that it is possible to provide the fail cylinder with an adequate retard angle.
According to the invention of claim 7, there is provided a knock control apparatus for internal-combustion engines specified in claim 6, wherein the retard angle changing means brings an amount of correction in ignition timing of a fail-judged cylinder close to the retard angle for the fail cylinder at a predetermined speed. According to such structure, there is an effect that it is possible to change to the target amount of correction in the ignition timing without abruptly changing the ignition timing.
According to the invention of claim 8, there is provided a knock control apparatus for internal-combustion engines specified in claim 1, wherein the normal judgment returning means judges that at least the retard angle of the fail cylinder is not a predetermined angle or more larger than the retard angles of the other cylinders, and that the filter value of the fail cylinder is equal to or less than the predetermined value, and stop failure judgment. According to such structure, there is an effect that it is possible to return to the original ignition timing control after whether or not knocking can be normally detected is verified.
According to the invention of claim 9, there is provided a knock control apparatus for internal-combustion engines specified in claim 8, wherein if a number of fail-judged cylinders is under a predetermined number of cylinders, when it stops failure judgment for any of the fail-judged cylinders, the normal judgment returning means replaces the retard angle of the cylinder concerned with a retard angle having the maximum value among retard angles of the cylinders, which have not been judged to be defective, and makes the retard angle of the cylinder concerned effective with respect to the ignition timing control. According to such structure, there is an effect that it is possible to start with the optimum retard control when returning to the original ignition timing control.
According to the invention of claim 10, there is provided a knock control apparatus for internal-combustion engines specified in claim 8, wherein if the number of fail-judged cylinders exceeds a predetermined number of cylinders, the normal judgment returning means stops failure judgment for some fail-judged cylinders; if the number of fail cylinders is under the predetermined number of cylinders, the retard angle for any cylinders other than the fail cylinders is replaced with a retard angle a predetermined angle smaller than the predetermined retard angle, and is made effective for the ignition timing control; and the retard angle for the fail cylinder is nullified for the ignition timing control, and the ignition timing of the cylinder concerned is corrected based on the maximum value among the retard angles of cylinders which have not been judged to be defective. According to such structure, there is an effect that any cylinders other than the fail cylinders can be returned to the ignition timing control based on the original knock control from the safety-side ignition timing control.
Further, according to the invention of claim 11, there is provided a knock control apparatus for internal-combustion engines specified in claim 10, wherein the predetermined angle is equal to an increase in the maximum retard angle which can be increased by one knock detection. According to such structure, there is an effect that even if the retard angle on returning to the ignition timing control using the original knock control should be insufficient for the occurrence of the knock, it is possible to return to the original safety-side retard angle by one great knock judgment.